This invention relates to the field of load transmission devices. More particularly, this invention relates to a self-aligning load transmission post for use with a plurality of bellows or other devices in an environment where there are critical requirements for the direction and location in which a load is imposed.
This invention is particularly intended to be an improvement in the construction of the self-aligning load transmission post disclosed in U.S. Pat. No. 4,012,084, which is assigned to the assignee hereof and incorporated herein by reference. U.S. Pat. No. 4,012,084 was intended, in part, to be an improvement over the construction of the mechanical torque wrench with hydraulic readout described in U.S. Pat. No. 3,683,686, which is assigned to the assignee of the present invention and incorporated herein by reference. Reference is hereby made to U.S. Pat. Nos. 4,012,084 and 3,683,686 for a full understanding of the environment and details thereof in which the preferred embodiment of this invention will be described.
The torque wrench of U.S. Pat. No. 3,683,686 has a hydraulic readout system to obtain meaurements of the torque being applied. That hydraulic readout system employs two hydraulic load cells, in the form of bellows, and a Bourdon gauge interconnected by hydraulic tubing, those elements being hermetically sealed and filled with a non-compressible fluid. As torque is applied with the wrench, reaction forces equal to output torque of the wrench are imposed on the bellows and measured on the Bourdon gauge to provide an accurate measurement of the torque output of the wrench.
Each bellow is mounted between a pair of opposed posts, and the reaction forces are applied to the bellows through these posts. Equalization of the loads on the bellows is critical for accurate readout of the torque load; and experience has shown that very close tolerances must be maintained on the alignment of the posts with each other and with the center line of the bellows to achieve this load equalization and accuracy in readout. While these tolerances can be realized, they increase the time and cost of manufacturing the wrench; and it has become highly desirable to find other ways of obtaining the desired load equalization.
U.S. Pat. No. 4,012,084 provides an improved post structure to the torque wrench of U.S. Pat. No. 3,683,686. In U.S. Pat. No. 4,012,084, self-aligning posts are provided which insure that the reaction loads will always be delivered through the center of the bellows and along the axis of the bellows. This assures equalization of the load on each of the bellows and accuracy of readout, notwithstanding gross misalignment between the center line of the posts with each other or with the axis of the bellows. The self-aligning posts of U.S. Pat. No. 4,012,084 are achieved by forming each of the posts in two separate parts. One part is a solid semispherical tip which engages a corresponding concave depression of larger radius in the bellows; and the other part is a main cylindricalsection which has a flat end to engage and bear against the flat portions of the semispherical tip. The bellows is retained between opposed self-aligning posts. This split configuration of the posts assures that the reaction forces of the wrench are delivered through the center of the bellows and along the bellows axis regardless of misalignment between the posts with each other or with the axis of the bellows.
While suitable for its intended purpose, the two separate parts of the self-aligning posts disclosed in U.S. Pat. No. 4,012,084 have a tendency to slip and disengage. In case of severe misalignment, the flat end of the semispherical tip may slip out of engagement with the flat end of the cylindrical post and may slip out of the socket in which the tip is located in the bellows. Any such slippage or disengagement is, of course, undesirable and presents adverse consequences.